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Digital Imaging Systems for Ballistics Testing

Saturday, 01 September 2012

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Traditionally, the recording of ordnance proofing data has been split into two main areas: instrumentation and high speed photography. Instrumentation was more focused on the collection of analytical data from various instruments, e.g. Doppler radar, yaw screens (for pitch and yaw), and velocity traps (i.e. skyscreens or acoustic triggers), whereas high speed photography was more concerned with obtaining high quality images for later qualitative analysis. The photographic images were obtained using an assortment of high speed film cameras, often requiring a specialist photographic team to survey in, set up and align the camera, illuminate the subject, synchronise the camera to the firing system, process the film records and produce the final images for later manual analysis.

From Film to Digital

Figure 1. Specialised Imaging SIR3 ballistic range cameraThe introduction of the Hadland Photonics BR553 high-speed ballistic digital range camera in 1988 marked the beginning of the demise of high-speed film cameras. These early cameras provided almost instant viewing of near photographic quality images. This allowed ballisticians and engineers to make changes to development rounds without having to wait sometimes several hours for films to be developed. The digital imaging systems also facilitated instant, on-site, measurement and analysis of ordnance performance. This, in turn, provided significant time savings that resulted in much faster firing rates being achieved and more productive use of range time.

The ensuing 25 years have seen the introduction of many major products which have helped revolutionize the way proofing and experimental ranges operate. Today the two main areas of recording ordnance proofing are instrumentation along with digital high speed imaging and post-production. Digital imaging, with the ability to post-process images, has now allowed the role, previously the preserve of dedicated photographers, to be fully integrated into the overall instrumentation suite. New image post-production operations, including ballistic/projectile performance, image/data analysis and collation, enable the trial data to be presented, within a very short time-frame, to the test sponsor/ordnance manufacturer in an accurately integrated format.

Double image of a projectile travelling at 800m/s.Since the introduction of the early ballistic range cameras, the quality and versatility of these instruments has gradually improved with advances in CCD sensor technology and improvements in image intensifiers (both of which are key elements in the capture of extremely short exposure still images). An example of a state-of-the-art ballistic range camera today is the SIR3 ballistic range camera (Figure 1). This new camera is capable of shutter speeds as short as 10ns, resulting in the elimination of motion blur in images of objects travelling at up to 4000 m/s. Offering 11 million pixel resolution images, the quality of results from the SIR3 is fast approaching film quality.

Nowadays, while a well-exposed and presented, sharp-focus picture is appreciated by ballisticians, their prime concern is the analytical data that can be derived from that image. This includes information such as projectile/fragment velocity, spin rates, pitch and yaw etc. With this in mind the SIR3 camera was developed with the unique ability to take a second full-resolution image (within 100us) so that analytical measurements taken from the images could be extended into the time domain without any loss of quality, and without the additional investment of a second camera. An added advantage of the second image facility is the ability to monitor projectile performance and integrity further into its flight path.

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